Reference to the past can be made in the following ways
should have been at the office before 9
I ought to have left London before 9
been leaving London before 9
be at the office before 9
I had to leave London before 9
be leaving London before 9
Should have and ought to have could be followed (here) by but I wasn t/l didn t to suggest that whatever was advisable or necessary did not happen / should have left London before 9 but I didn't
Had to suggests that the action was performed in the past because this was necessary It could be followed by and I was did I had to leave London before 9 and I did
The form had got to also exists, but it is not always suitable, had to is generally preferred
When other tenses are required, appropriate forms of have to must be
used to fill the gaps of the defective modal must [> 11.4]
/ have had to remind him several times to return my book
Because of the bus strike I've been having to walk to work every d i
The reason for our late arrival was that we had had to wait for
hours while they checked the plane before take off
If he had asked me I would have had to tell him the truth
Lack of necessity inadvisability prohibition
Lack of necessity, inadvisability, prohibition
Examples of modal forms to express inadvisability, etc.
Present lack of necessity past lack of necessity
You needn't go there You needn t have gone there
Or You don't need to go there (= you went there unnecessarily)
You don t have to go there You didn t have to go there
You haven t got to go there Or You didn t need to go there
(= there was no necessity to go there, whether you did go or not)
Present inadvisability past inadvisability, not acted upon
You shouldn t start smoking You shouldn t have started smoking
You ought not to start smoking You oughtn t to have started smoking
(but e g you ignored this advice)